As generally known in the art, cutting tools are used to cut ferrous metals, non-ferrous metals, and nonmetallic materials. The cutting tools are mounted to machine tools to cut a workpiece into a desired shape. Usually, a cutting tool is composed of a cutting insert which has cutting edges and a tool body to which the cutting insert is fastened.
Cutting tools are divided into brazing type cutting tools and indexable type cutting tools depending upon a method for fastening the cutting insert to the tool body. In the brazing type cutting tools, the cutting insert is permanently brazed to a portion of the tool body. In the indexable type cutting tools, the cutting insert is mounted to and dismounted from the tool body by fastening means arranged on the tool body.
In the indexable type cutting tools, when the available lifetime of the cutting edges of the cutting insert ends, since the cutting insert can be simply replaced with new one within a short time, it is possible to cope with the disadvantage of the conventional brazing type cutting tools, that a highly skilled person must re-grind the cutting edges of the cutting insert. For this reason, the indexable type cutting tools are currently adopted in most cutting tools.
There are two methods for cutting a metal using a cutting tool. In a first method, the cutting edges of a cutting tool which is fixedly held are brought into contact with a workpiece made of a metallic material, which is rotated, to perform a cutting function. In a second method, after a tool having cutting edges, that is, a cutting insert is fastened to a machine tool using a holder, the cutting tool is rotated to be brought into contact with or pass through the workpiece which is fixedly held, to machine the workpiece into a desired shape.
A drilling technique belongs to the second method as described above. In a drilling method, with a workpiece fixedly held, a drilling tool is rotated to create a hole through the workpiece.
Recently, when compared to an integrated solid drilling tool which is integrally formed of one material and has a drill body, flutes and cutting edges, an indexable type drilling tool in which a cutting insert is replaceably fastened to a drill body is widely used as a drilling tool. A configuration of the indexable type drilling tool has been changed from one in which a plurality of cutting inserts are fastened to the circumferential outer surface of the distal end of the drill body to another in which only one cutting insert is fastened across the distal end of the drill body.
However, the conventional indexable type cutting tool suffers from defects as described below. First, when fastening the cutting insert to the drill body, due to misalignment of the centers between the drill body and the cutting insert, precise setting cannot be ensured, whereby a machining precision cannot but be degraded when compared to the conventional solid type drilling tool.
Second, in order to precisely set the rotation centers of the cutting insert and the drill body, because a separate centering device is needed, a procedure for manufacturing the indexable type cutting tool is complicated, and a manufacturing cost increases.
Third, when coupling the cutting insert to the drill body, it is difficult to administrate an assembling precision.